Acetonitrile must be of an exceptionally high purity for use in UV spectrophotometry, electroanalytical studies, lithium-sulfur batteries, high performance liquid chromatography and DNA synthesis. In particular, acetonitrile must be exceptionally pure for these uses with regard to such as UV absorbing materials and water. Prior art methods of purifying acetonitrile have been unsatisfactory for a variety of reasons. One reason is that the methods generally involve at least one stage of distillation. A distillation stage is both costly in capital and operating costs and inefficient due to high losses e.g. in the bottoms of the stills if usual oxidation methods are used. The process of purification of the present invention does not use a single distillation stage yet achieves exceptional purity of low water content in the product, great capital savings at substantially no impact on environment because of substantially no wastes, and at great energy savings.
There are many other disadvantages of the prior art methods which are overcome by the present invention. For example, the process of the present invention does not use corrosive chemicals such as amines or environmentally detrimental compounds such as permanganates, and the purity of the acetonitrile which is achieved is somewhat higher according to the process of this invention than with any prior art methods known to the inventors. The product is substantially impurity "finger print" free and is achieved without the asymptotically raising costs (and effort) associated with the prior art required to achieve the same purity level.
One source of acetonitrile is from the production of acrylonitrile by gas phase oxidation of propylene and ammonia with oxygen. Acetonitrile is a by-product of the production of acrylonitrile, and as such may be highly impure depending, for example, upon the mode of operation of the acrylonitrile plant and the method of clean-up for the by-product acetonitrile. Typical of the impurities associated with acetonitrile include at least one or more of the following: oxazole, acrylonitrile, crotonitrile, methacrylonitrile and perhaps methyloxazole. Water is also present in acetonitrile. Additional impurities are also likely to be present, again depending on the process conditions experienced in the production of acrylonitrile, the source of acrylonitrile and the partial purification steps attempted. One of the undesirable class of impurities are aromatic compounds and for sake of greater efficiency this invention also relates to the removal of aromatic impurities from acetonitrile.
A number of prior attempts to purify acetonitrile have been carried out but have not been satisfactory as noted above. The potential or ultimate amount and quality of purified acetonitrile which can be recovered is a goal against which all attempts have been measured. This ultimate goal has eluded many attempts, especially on an industrial scale.